The present invention is an address mapping gateway, used in an internetwork link, that associates all nodes in a domain with a single network number (referred to as a domain network address), and provides gateway-mapped node addresses that are unique within the domain. The address mapping gateway dynamically substitutes the "globally-unique" domain network address and the "domain-unique" gateway-mapped node address for a network number and node address, respectively, of a network layer address of a packet header received from a source node in the domain. Conversely, when a packet is received for a destination node in the domain, the address mapping gateway substitutes the originally-assigned network number and node address for the domain network address and gateway-mapped node address, respectively, prior to forwarding the packet to the node. Specifically, the address mapping gateway maintains an address mapping table that provides a cross-reference between (1) a source node address and the network number of the local network in which the node resides, and (2) a gateway-mapped node address generated by the address mapping gateway. Upon receipt of a packet from the source node, the address mapping gateway creates a mapping entry in the address mapping table that node and performs an address translation to a globally-unique network layer address. On the other hand, upon receipt of a packet destined for a destination node in the domain, the address mapping gateway locates the mapping entry for the packet's gateway-mapped node address and performs a reverse address translation to the originally-assigned network layer address.